In my observations, using the <P extends object> generic in JavaScript is often deemed pointless since virtually everything in the language is an object. Most literals behave like objects with methods such as .toString, and strings are objects with properties like .length. Personally, I tend to opt for simply <P>, but I am interested in hearing others' perspectives on this.
While I don't have a specific example to share at the moment, I'm eager to learn from others' experiences.
For further details, check out "The object Type in TypeScript".
The object type introduced in TypeScript serves the purpose of excluding the seven primitive types, such as string, number, boolean, bigint, symbol, undefined, and null. Even though
typeof null === "object"string, number, boolean, bigint, and symbol are automatically wrapped in respective objects (String, Number, Boolean, BigInt, Symbol) when accessing their members as if they were objects, they are distinguishable from true objects, making a difference in certain scenarios. One example mentioned in the TypeScript Handbook is Object.create(), which generates runtime errors when passed an argument of a primitive type (aside from null). Therefore, for functions like Object.create(), TypeScript specifies that its argument should be of type object | null. To exclude primitives in a generic parameter, using <P extends object> is the correct approach, proving its significance.
Note that TypeScript also includes an interface named Object, starting with an uppercase O, containing apparent members that exist on everything in JS, such as valueOf() and toString(). Although this interface might align more closely with the concept of "everything is an object," only null and undefined cannot be assigned to Object. Generally, opting not to utilize the Object type in TypeScript, as wrapper types are rarely preferred by developers, is advisable.
In case you aim to encompass "anything that can be indexed into like an object," employing the so-called "empty object" type, {}, is recommended. This object type possesses no known properties and operates similarly to Object, with only null and undefined being exceptions. It was previously the case that unconstrained generic type parameters were implicitly constrained to {}, hence rendering <P extends {}> virtually arbitrary.
However, since TypeScript 3.5, unconstrained generics now receive an implicit constraint of unknown instead of {}. The unknown type truly embodies "everything" in TypeScript. Basically, any value can be assigned to a variable of type
unknown</code (though vice-versa isn't permissible). Specifying <code><P extends unknown>Lastly, we point towards any, representing the ultimate "anything-goes" type. Not only does any allow assigning any value (akin to
unknown</code), but it also permits assigning <code>anynever</code). Resorting to <code>any<P extends any> equals to working with <P extends unknown>, rendering them equally superfluous. The prior functionality of allowing P to resemble any under unresolved circumstances through <P extends any> was considered impractical and thus modified.
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